星际介质礼赞 Anthem of ISM

（抱歉没精力细抠中文，只能先押英文韵了）

1. The spin-flip line reveals atomic gas,

飞旋的谱线揭示出原子气体，

Which fills the space and holds a lot of mass.

填满了空间，占据了质量。

New stars are born in clouds we can’t directly see,

新星诞生于我们无法直视的云中，

We get around this by observing states of C.

通过观测碳的状态才得知其性质。

Warm bubbles of dense gas encase each massive star,

致密气体的温暖泡泡裹住了每颗大质量恒星，

But their ionizing light still makes it pretty far.

但是电离的光子还是让它远远退避。

The light from these young stars runs headlong into dust,

年轻恒星的光线扎进尘埃，

To trace these grains, IR emission is a must.

要追踪那些微粒，必须要靠红外辐射。

When massive stars explode, they blast the gas away,

当大质量恒星爆炸，它们把气体炸开，

And shock what’s left to upwards of a million K.

激波把剩下的东西加热到一百万开尔文。

Last, while this disk of gas can let the system grow,

还有，尽管气体盘面可以让星系生长，

It’s still not much compared to the halo ...

它还是无法和暗物质晕相比……

2. At z of naught, HI’s the bulk of gas by far,

在红移为零时，中性氢占目前气体的大头，

A little dwarf can even have more gas than stars,

一颗小矮星系的气体甚至比恒星还要多，

Fractionally, the H2 remains quite low,

从比例上来说，氢分子相当少，

Though in detail this depends on XCO,

尽管具体来说这取决于转换因子，

Clusters strip gas and major mergers make it dense,

星系团抽出气体，主并合将其压缩，

And early types have gas but just a few percents,

早型星系有气体但只占几个百分点，

The metal content follows from the system’s weight,

金属元素含量跟着系统的质量走，

With little dwarfs at metallicities of eight,

矮星系的金属丰度在八左右，

Solids? The dustiness tracks metallicity,

固体？富尘埃与否追踪的是金属丰度，

But with a steep dependence, leaving dwarfs dust-free.

但是依赖关系很陡峭，让矮星系没有了尘埃。

3. As an exponential disk both CO and starlight fall,

一氧化碳和星光都以指数形式沿盘下降，

While HI at a nearly fixed N(H) just sprawls,

而中性氢以几乎不变的柱密度四处弥散，

A stellar bar can cause a deviation from this scheme,

恒星棒会导致星系偏离这种情况，

Since gas inflow can make the center quite extreme.

因为气体内流会让中心特别激动。

Now the cold gas in the inner disk – it lies in a thin layer,

现在来看中心盘面的冷气体——它位于一个薄层上，

But at large “r” with fewer stars, the HI disk does flare.

但是在恒星寥寥的大半径处，中性氢盘面确实在闪耀。

Increasing radius, it also drops the metal count,

半径增大，金属也减少，

Which may go down by point three dex before the stars run out.

在恒星消失之前能降低零点三个因子。

That H2 gas, of course, its clumped up in GMCs,

氢分子气体，当然，缩在巨分子云中，

Cold, dense clouds that play the role of stellar nurseries,

那是冷而致密的云团，扮演恒星育婴室的角色，

The speed with which that cold, dense gas supply gets ate,

那冷而致密的气体供给被吞噬的速度，

It varies as function of the mass and star formation rate.

随着质量和恒星形成速率变化。

So – that’s my low-z ISM collection,

那么——这就是我的低红移星际介质收藏，

Now to you – I ask for questions and corrections?

现在该你了——有什么问题或指教？